The present invention concerns a method of and device for optimizing the unproductive motions of the holdfast beam in a machine that cuts material, especially stacked sheets of paper, cardboard, etc.
In a known machine for cutting such material the sheets are stacked on a bench and a hydraulic beam descends onto the stack to hold it fast. Once the cut has been produced, the beam rises into an invariable upper position. The distance between the holdfast beam in that position and the surface of the bench slightly exceeds maximal height of the stack of material.
There is a drawback to such a machine in that the holdfast beam executes unproductive motions when a low stack is processed. Considerable time is lost while the beam descends onto the stack from its upper position. Raising the beam to its upper position once the cut has been produced also takes considerable time. These long intervals considerably decelerate the overall process when the machine is operating automatically, The material cannot be advanced along the surface until the beam is all the way up. The blade's and the beam's unproductive motions can in particularly last longer than it takes to advance a stack of small sheets, labels for example.
German AS 1 190 431 discloses not raising the hydraulically operated beam and blade in a machine that cuts material, especially stacked sheets of paper, cardboard, or similar material as unprofitably high as is necessary in a machine that is driven by a crankshaft. The material can accordingly be advanced in this embodiment as soon as the blade and beam release the stack.
German AS 1 095 254 discloses switching circuitry for a machine that cuts material, especially stacked sheets of paper, cardboard, or similar material with a blade-accommodating beam and a mechanically controlled automatically operated holdfast beam. The holdfast beam is lifted out of the position in which it holds down the material by a device that actuates the beam's mechanisms and responds to the arrival of the blade-accommodating beam at a specific elevation. The device comprises a switch that includes a roller and a sloping surface that the roller rolls over, controlling the switch. The holdfast pressure is removed when the blade rises above the stack, which is precisely when the holdfast beam begins to rise. The upward motion of the holdfast beam is accordingly dictated by the upward motion of the blade, but the distance traveled by the holdfast beam is not dictated by the height of the stack.